1. Field of Invention
This invention relates to obtaining image shear and/or skew values for performing image revisions.
2. Description of Related Art
An affine transformation is a transformation which preserves the parallelism of lines in input and output images. One application of affine transformations is in image input operations, such as scanning operations. Specifically, image input systems may have slight imperfections which result in a slight errors in the input image.
FIG. 1 shows an original image 12 on an image bearing substrate 10. When the image 12 is scanned by a scanner of the type which transports the substrate 10 past a scan head, the scanner may impart shear and/or skew to the scanned representation of the image. “Shear” is a location dependent shifting of an image which results from non-perpendicularity of the motion of a substrate relative to device such as a scan head. As shown in FIG. 2, this results in an image 12 that is distorted, compared to the original image 12 shown in FIG. 1. Thus, a distorted image 12 is subsequently output by being printed on a substrate 20, displayed on a screen, and/or the like.
Shear may be caused by, for example, an error in the alignment of a scan head with respect to a document feeder chassis, an error in the alignment of a paper drive shaft relative to the document feeder chassis, or the like.
“Skew” refers to an accidental, usually slight, rotation of an image that occurs due to rotation of an image bearing substrate relative to a device such as a scan head. Most document feeders in scanners and copiers, especially high-speed document feeders, are susceptible to at least some degree of skew. As shown in FIG. 3, skew results in an image 12 that is slightly rotated, compared to the original image 12 shown in FIG. 1. Thus, a slightly rotated image is subsequently output by being printed on a substrate 20, displayed on a screen, and/or the like.